Cardiac pacemaker wireless energy supply system based on three-dimensional mixed magnetic conductivity metamaterial

Abstract

The invention discloses a cardiac pacemaker wireless energy supply system based on a three-dimensional mixed magnetic conductivity metamaterial. The method comprises the following steps: determining geometric parameters of a three-dimensional mixed magnetic conductivity metamaterial element according to the geometric shape of an implantable cardiac pacemaker; optimizing the thickness of the substrate and the number of turns of the coil according to the transmission efficiency of the system; determining the external lumped capacitance and verifying the negative magnetic conductivity characteristic of the electromagnetic metamaterial; four meta-materials with near-zero magnetic conductivity are placed on the periphery of a transmitting coil, a negative magnetic meta-material is placed between the transmitting coil and a receiving coil, and the negative magnetic meta-material and the meta-materials with near-zero magnetic conductivity are combined to form a cubic three-dimensional mixed magnetic conductivity meta-material. By means of the design method, efficient magnetic field convergence and magnetic leakage shielding of the wireless energy supply system of the implantable cardiac pacemaker can be achieved, and wireless energy supply development of implantable devices is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless energy transmission, and particularly relates to a wireless power supply system for a cardiac pacemaker based on three-dimensional hybrid permeability metamaterials, which is applicable to the efficient wireless power supply and magnetic leakage suppression of medical implant devices (such as cardiac pacemakers). Background Art

[0002] A cardiac pacemaker is an implantable medical device used to help maintain a patient's heart rhythm through electrical signals. However, traditional cardiac pacemakers usually rely on built-in batteries for power supply, and the battery life is limited. Patients need to undergo surgery to replace the battery regularly, which not only increases the surgical risk but also brings pain and inconvenience to the patients. The core of the magnetic coupling resonance wireless energy transmission technology is to use electromagnetic waves for energy transmission, which can avoid the use of cables or wires. Therefore, the application of wireless power transmission technology to implantable cardiac pacemakers can effectively avoid the above risks. However, in practical applications, problems such as an increase in the transmission distance and misalignment between coils often occur. These problems will reduce the magnetic coupling between the transmission coils, resulting in a decrease in the transmission efficiency of the system. Moreover, since the transmission coils use electromagnetic waves for energy transmission, the electromagnetic field leakage will also cause harm to the human body.

[0003] Traditional methods for enhancing the transmission efficiency of the MCR-WPT system usually require increasing the number of coils or increasing the coil size, which will lead to an increase in the device volume, and thus the MCR-WPT system is no longer suitable for implantable devices; traditional methods for reducing the magnetic leakage of the MCR-WPT system use metal shielding layers to suppress external electromagnetic interference, such as ferrite, etc., but it will increase the eddy current loss and reduce the transmission efficiency of the system. Electromagnetic metamaterials are a new type of artificial composite material with special physical properties. By artificially designing its periodic structural units, properties such as negative magnetic permeability, negative permittivity, negative refractive index, and evanescent wave amplification can be realized. Electromagnetic metamaterials with negative magnetic permeability can direct the magnetic field towards the receiving coil, enhance the transmission efficiency of the MCR-WPT system while constraining the magnetic field; electromagnetic metamaterials with magnetic permeability close to zero can completely shield non-vertically incident waves and reflect them, reducing the magnetic leakage of the MCR-WPT system.

[0004] Chinese Invention Patent Publication No. 202111572456.1 discloses an adjustable electromagnetic metamaterial design method for wireless charging of power equipment. This patent design does not consider the damage caused by magnetic leakage to electronic devices. Based on this, a wireless energy transmission system is designed with the goal of improving the transmission efficiency and reducing the harm of magnetic leakage. Summary of the Invention

[0005] The present invention proposes a wireless power supply system for a cardiac pacemaker based on three-dimensional hybrid permeability metamaterials, aiming to solve the problems in the prior art that it is difficult to balance efficiency and leakage magnetic field suppression, and the anti-offset ability is poor, while improving the stability and biosafety of the wireless power supply system for the cardiac pacemaker.

[0006] To achieve the above objectives, the present invention adopts the following steps. Step 1: Reasonably design the size of the unit cell of the three-dimensional hybrid permeability metamaterial with the size of the cardiac pacemaker as a parameter. Print the square spiral metal structure on the FR4 epoxy resin substrate. At the bottom of the substrate, realize the series connection of the lumped capacitor and the metal open square spiral loop through vias. Step 2: Under the condition of determining the line width, line gap, and outer diameter size, optimize the thickness of the FR4 epoxy resin substrate and the number of turns of the square spiral metal coil by the method of controlling variables. Step 3: The electromagnetic metamaterial adjusts the resonance frequency by an external capacitor, and determines the size of the external capacitor according to the magnetic permeability of the electromagnetic metamaterial at the operating frequency of the implantable cardiac pacemaker, and verifies the negative magnetic permeability characteristic of the metamaterial. Step 4: Determine the diameters of the transmitting coil and the receiving coil and the distance between the two coils according to the size of the electromagnetic metamaterial unit cell and the position of the implantable cardiac pacemaker in the human body. Surround the four sides of the receiving coil with 4 designed near-zero magnetic permeability metamaterial unit cells, and place 1 designed negative magnetic permeability metamaterial unit cell between the receiving coil and the transmitting coil. The 5 metamaterials form a cube three-dimensional hybrid permeability metamaterial, and apply it to the MCR-WPT system.

[0007] With the above solution, when the MCR-WPT system starts to operate, the negative magnetic permeability metamaterial unit cell will collect the stray electromagnetic waves to the receiving coil, thereby improving the transmission efficiency of the MCR-WPT system. Since the transmitting coil is surrounded by the near-zero magnetic permeability metamaterial, when the non-perpendicular electromagnetic wave contacts the near-zero magnetic permeability metamaterial, it will be totally reflected back. Part of the non-perpendicular electromagnetic wave will be reflected onto the negative magnetic permeability metamaterial unit cell and then be converged to the receiving coil by the negative magnetic permeability metamaterial unit cell, effectively shielding the leakage magnetic field around the reflection coil and enhancing the transmission efficiency of the MCR-WPT system for the second time. Further, in Step 1, the side length L of the unit cell of the three-dimensional hybrid permeability metamaterial is determined with the size of the implantable cardiac pacemaker as a parameter. aThe maximum side length of the square spiral coil is 30 mm and the maximum side length d0 of the square spiral coil is 26 mm. Further, in step 2, the wire width w of the square spiral metal coil is determined to be 0.5 mm and the turn spacing s is 0.25 mm according to the actual manufacturing process of the actual PCB electromagnetic metamaterial board. Further, in step 2, the control variable method is used to optimize the number of turns of the square spiral metal coil of the metamaterial and the thickness of the FR4 epoxy resin substrate, and the optimized square spiral metal coil of the metamaterial is printed on the optimized FR4 epoxy resin substrate. Further, in step 3, the sizes of the external lumped capacitors of the two electromagnetic metamaterials are obtained according to the number of turns of the optimized square spiral metal coil of the metamaterial and the substrate thickness, and the square spiral metal coil is connected in series with the external lumped capacitor through vias. Further, the negative magnetic permeability of the metamaterial electromagnetic metamaterial is specifically reflected in that when its operating frequency is around the resonance frequency, the current distribution in the element reverses. Therefore, electromagnetic simulation research is carried out on the electromagnetic metamaterial according to the optimized parameters of the electromagnetic metamaterial to determine whether it has the characteristic of negative magnetic permeability. Further, in step 4, the two optimized electromagnetic metamaterials in step 2 are combined. One electromagnetic metamaterial with negative magnetic permeability and four electromagnetic metamaterials with near-zero magnetic permeability are combined into a cube without a lid, and the four sides of the electromagnetic metamaterial with negative magnetic permeability are all connected to the electromagnetic metamaterials with near-zero magnetic permeability. Further, in step 4, the diameters of the transmitting coil and the receiving coil are designed according to the size of the metamaterial. Further, in step 4, the distance between the transmitting coil and the receiving coil is determined according to the position where the implantable cardiac pacemaker is installed in the human body in practice. Further, in step 4, the transmitting coil is placed inside the three-dimensional hybrid magnetic permeability metamaterial, the transmitting coil is directly opposite to the element of the electromagnetic metamaterial with negative magnetic permeability, the receiving coil is placed outside the three-dimensional hybrid magnetic permeability metamaterial, and is also directly opposite to the element of the electromagnetic metamaterial with negative magnetic permeability. The two coils are at the same horizontal height.

[0008] In summary, the beneficial effect of the present invention is that the near-zero magnetic permeability metamaterial unit is placed around the transmitting coil. Compared with other shielding effects that only utilize the near-zero magnetic permeability metamaterial, the present invention also utilizes its electromagnetic total reflection characteristic to reflect part of the electromagnetic wave that should have been shielded back to the element of the negative magnetic metamaterial, and finally refracts it to the receiving coil, realizing a secondary improvement in the transmission efficiency of the system. In order to be able to more clearly understand the technical means of the present invention and to be implemented in accordance with the content of the specification, and in order to make the purpose, features and advantages of the present invention more obvious and understandable, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0009] Figure 1 It is a schematic structural diagram of an electromagnetic metamaterial resonant unit; Figure 2 Transmission efficiency curves at different numbers of turns and substrate thicknesses; Figure 3 Equivalent magnetic permeability curve of the electromagnetic metamaterial; Figure 4 Verification diagram of negative permeability characteristics; Figure 5 Schematic diagram of a WPT system based on three-dimensional hybrid permeability metamaterials; Figure 6 Design flow chart of three-dimensional hybrid electromagnetic metamaterials. Specific implementation manners

[0011] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the protection scope of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0012] The present invention provides a design method of three-dimensional hybrid electromagnetic metamaterials for wireless charging of implantable cardiac pacemakers. Figure 6 It is a block diagram of the method steps for designing three-dimensional hybrid metamaterials. As Figure 6 shown, the design method of three-dimensional electromagnetic metamaterials for wireless charging of cardiac pacemakers includes the following steps: (1) Determine the side length L of the unit cell of the three-dimensional hybrid permeability metamaterials with the size of the implantable cardiac pacemaker as a parameter a and the maximum side length d0 of the square spiral coil, and determine the coil wire width w and the turn spacing s according to the actual manufacturing process. (2) Optimize the thickness of the substrate and the number of turns of the coil. (3) Determine the size of the external lumped capacitor and verify the negative permeability characteristics of the electromagnetic metamaterials. (4) Combine different electromagnetic metamaterial unit cells into three-dimensional hybrid metamaterials and apply them to the MCR-WPT system.

[0013] Aiming at the problems of difficult balance between efficiency and leakage magnetic field suppression and poor anti-offset ability in the wireless power transfer technology of implantable cardiac pacemakers, and combining with the size parameters of implantable cardiac pacemakers, the following design method is given. The implantable cardiac pacemaker is very small. Through the close arrangement of coils, the planar spiral structure can achieve a relatively high inductance value within a limited area, and the symmetry of the spiral makes its magnetic field distribution more uniform, which is conducive to improving the coupling efficiency of wireless energy transfer. Therefore, the planar spiral structure based on printed circuit board technology can be adopted. The square structure is easier to be closely arranged in the planar layout, especially suitable for scenarios requiring high-density integration. There are gaps between circular coils, and it is difficult to achieve high-density integration during planar layout, resulting in a large occupied area. The symmetry of the square structure makes the change of magnetic field distribution relatively uniform during horizontal offset, while the symmetry of the circular structure leads to a rapid decline in magnetic field coupling during horizontal offset, and the offset tolerance is usually smaller than that of the square structure. The square coil can be directly etched through the printed circuit board (PCB) process, with low processing cost and suitable for mass production. Precision circular coils (especially those in the micron level) require laser cutting or lithography processes, with high costs and great difficulty in mass production. Considering the above factors, the three-dimensional hybrid electromagnetic metamaterial design for wireless charging of implantable cardiac pacemakers will be based on the planar square spiral structure.

[0014] Figure 1 Figure 4 shows the structure diagram of the square spiral electromagnetic metamaterial. The square spiral metal structure is printed on the FR4 epoxy resin substrate. At the bottom of the substrate, the lumped capacitor is connected in series with the metal open square spiral ring through vias. Among them, L a is the width of the FR4 substrate of the metamaterial, d i is the outer diameter of the coil, d0 is the inner diameter of the coil, w is the width of the coil wire, s is the turn spacing, and h is the thickness of the substrate.

[0015] The equivalent inductance and equivalent capacitance of the electromagnetic metamaterial are calculated by formula (1) and formula (2).

[0016] The resonant frequency of the metamaterial unit is calculated by formula (3).

[0017] The AC impedance of the coil can be obtained from formula (4).

[0018] The equivalent permeability of the metamaterial is calculated by formula (5).

[0019] where L is the equivalent inductance of the electromagnetic metamaterial in H; μ0 is the magnetic permeability of vacuum; di is the outer diameter of the coil; d0 is the inner diameter of the coil. C is the equivalent capacitance of the electromagnetic metamaterial; ε0 represents the vacuum permittivity; s is the turn spacing of the electromagnetic metamaterial; n is the number of coil turns; f is the resonant frequency of the metamaterial unit; C0 is the external lumped capacitance; ρ c is the resistivity of the metal material; l c is the total length of the coil; t c is the thickness of the metal material,; δ is the skin effect coefficient; C z is the sum of the self-capacitance of the resonant unit and the external lumped capacitance; L a is the width of the FR4 substrate of the metamaterial. The above formulas establish the relationship between the structural parameters of the electromagnetic metamaterial, the resonant frequency, and the negative permeability characteristics of the electromagnetic metamaterial, which can provide a basis for the optimal design of the electromagnetic metamaterial structure.

[0020] First, determine the size of the square spiral coil according to the actual requirements of the system, that is, determine the width of the FR4 substrate of the metamaterial as L a , the outer diameter of the coil is d i , and determine the wire width w and turn spacing s of the square spiral metal coil according to the actual manufacturing process of the actual PCB electromagnetic metamaterial board. When the number of coil turns n takes different values, each number of coil turns n corresponds to a unique external lumped capacitance under the magnetic permeability at the same operating frequency. Similarly, the substrate thickness is also the same. Based on this, the optimal value should be selected for each group. The maximum size of the square coil required by the actual demand is L a = 30mm, d i = 26mm. Determine the coil wire width w = 0.5mm and turn spacing s = 0.25mm according to the actual manufacturing process of the PCB metamaterial board. Keeping the above parameters unchanged, optimize the number of turns of the square spiral coil and the substrate thickness. The optimization results are as follows Figure 2a and Figure 2b shown. When the number of turns N changes from 3 turns to 12 turns, the transmission efficiency of the MCR-WPT system using the square spiral structure electromagnetic metamaterial first increases and then decreases, and the system transmission efficiency is the highest when the number of turns is 9; when the substrate thickness changes from 0.7mm to 1.3mm, the transmission efficiency of the MCR-WPT system using the square spiral structure electromagnetic metamaterial first increases and then decreases; the system transmission efficiency is the highest when the substrate thickness is 1mm.

[0021] After the structural parameters of the square spiral structure electromagnetic metamaterial are determined, the size of the external capacitance can be calculated through a fixed operating frequency of 6.78MHz. When the magnetic permeability is close to -1, the external capacitance is 260pF, and when the magnetic permeability is close to 0, the external capacitance is 300pF. The equivalent magnetic permeability curve is as follows Figure 3 shown. The negative permeability characteristic of the unit is specifically reflected in that when its operating frequency is before and after the resonant frequency, the current distribution in the unit is reversed. As Figure 5As shown in the figure, at 5.5MHz, the current direction in the unit cell is counterclockwise, and at 7MHz, the current direction in the unit cell is clockwise. The designed square spiral structure electromagnetic metamaterial has a magnetic permeability of nearly zero and -1 at an operating frequency of 6.78MHz, and its size is only 30mm×30mm, which meets the miniaturization requirements of the wireless charging system of implantable cardiac pacemakers. The above pin implantable cardiac pacemaker size gives the optimization design method of the square spiral structure electromagnetic metamaterial structure.

[0022] Since the transmitting coil is to be placed in the three-dimensional hybrid permeability metamaterial, the diameter of the transmitting coil must be smaller than the circumference of the electromagnetic metamaterial element. At the same time, it is also necessary to meet the size requirements of the implantable pacemaker, so the diameter of the transmitting coil and the receiving coil is determined to be 26 mm. Implantable pacemakers are usually installed under the skin of the human chest (the area below the clavicle), and the depth from the skin surface is generally about 10 mm. In order to make the pacemaker wireless power supply system based on three-dimensional hybrid permeability metamaterial universal, the horizontal distance between the transmitting coil and the receiving coil is determined to be 20 mm, and the coils are aligned in the horizontal direction. The two electromagnetic metamaterials are combined into a three-dimensional hybrid permeability metamaterial, such as Figure 5 As shown on the left, four near-zero magnetic metamaterial elements and one negative magnetic permeability metamaterial element are combined into a cube without a lid, in which the negative magnetic permeability metamaterial element is connected to all four near-zero magnetic metamaterial elements, and the near-zero magnetic metamaterial elements are connected in pairs. The transmitting coil is placed in the three-dimensional hybrid magnetic permeability metamaterial and faces the negative magnetic permeability metamaterial element. The horizontal distance between it and the negative magnetic permeability metamaterial element is 10 mm, and the vertical distance between it and each near-zero magnetic metamaterial element is 2.5 mm. The receiving coil is placed outside the three-dimensional hybrid magnetic permeability metamaterial and faces the negative magnetic permeability metamaterial element. It is aligned with the transmitting coil and has a horizontal distance of 10 mm from the negative magnetic permeability metamaterial element. When the system starts working, the trend of the electromagnetic wave is as follows: Figure 5 As shown in the upper right figure, the negative magnetic permeability metamaterial element in the three-dimensional hybrid magnetic permeability metamaterial converges the electromagnetic waves that should have been dispersed into the receiving coil, thereby enhancing the transmission efficiency of the system; the near-zero magnetic permeability metamaterial element in the three-dimensional hybrid magnetic permeability metamaterial totally reflects the non-vertical incident waves inside it, shielding the leakage magnetic flux generated by the system, and also reflecting part of the leakage magnetic flux to the negative magnetic metamaterial, which is then converged to the receiving coil through the negative magnetic metamaterial, achieving a secondary improvement in transmission efficiency.

[0023] The innovation of the present invention lies in the use of a three-dimensional hybrid magnetic permeability electromagnetic metamaterial in the pacemaker wireless power supply system. Based on the magnetic focusing effect of the negative magnetic metamaterial and the reflection effect of the near-zero magnetic metamaterial, the transmission efficiency of the system is greatly improved, the magnetic field leakage is reduced, and the harm of leakage magnetic field to the human body is reduced.

Claims

1. A wireless power supply system for a cardiac pacemaker based on three-dimensional hybrid permeability metamaterials, characterized in that, It includes the following steps: (1) Reasonably design the size of the three-dimensional hybrid permeability metamaterial unit cell and the maximum side length of the square spiral coil according to the size of the cardiac pacemaker; (2) Optimize the thickness and number of turns of the substrate according to the equivalent permeability calculation formula of the resonator unit of the square spiral coil; (3) Determine the size of the external capacitor according to the permeability of the electromagnetic metamaterial at the operating frequency of the cardiac pacemaker and verify the negative permeability characteristic of the metamaterial; (4) Place the near-zero magnetic permeability metamaterial unit cells around the transmitting coil, place the negative magnetic permeability metamaterial unit cells in the middle of the transmitting and receiving coils, and form a cube with the near-zero magnetic permeability metamaterial.

2. The system according to claim 1, wherein In step (1), the side length L of the unit cell of the three-dimensional hybrid permeability metamaterial is determined with the size of the implantable cardiac pacemaker as a parameter. a It is 30 mm.

3. The system according to claim 1, characterized in that, In step (1), determine that the planar spiral structure of the printed circuit board is a square spiral metal coil according to the designed size of the metamaterial unit cell, and determine that the maximum side length d0 of the square spiral coil is 26 mm.

4. The system according to claim 1, wherein In step (1), determine that the wire width w of the square spiral metal coil is 0.5 mm and the turn spacing s is 0.25 mm according to the actual manufacturing process of the actual PCB electromagnetic metamaterial board.

5. The system according to claim 1, wherein In step (2), use the method of controlling variables to optimize the number of turns of the coil and the thickness of the substrate of the electromagnetic metamaterial respectively, determine their optimal values, and print the optimized square spiral coil on the FR4 epoxy resin substrate with the optimized substrate thickness.

6. The system according to claim 1, wherein In step (3), determine the external capacitors of the near-zero magnetic permeability electromagnetic metamaterial and the electromagnetic metamaterial with a permeability of -1 according to the operating frequency of the implantable cardiac pacemaker, and connect the external capacitors under the FR4 epoxy resin substrate in series with the square spiral coil through vias.

7. The system according to claim 1, wherein In step (3), verify the negative permeability characteristic of the electromagnetic metamaterial after determining the size of the external lumped capacitor of the electromagnetic metamaterial.

8. The system according to claim 1, wherein In step (4), determine that the diameters of the transmitting coil and the receiving coil are 26 mm according to the size of the electromagnetic supermagnetic material unit cell.

9. The system according to claim 1, wherein In step (4), determine the distance between the two coils according to the actual placement position of the implantable cardiac pacemaker in the human body. Align the transmitting coil and the receiving coil horizontally, and the horizontal distance between the two coils is 20 mm.

10. The system according to claim 1, wherein In step (4), in the magnetic coupled resonant wireless power transfer (MCR-WPT) system composed of the transmitting coil and the receiving coil, place the designed 4 near-zero magnetic permeability metamaterial unit cells horizontally around the transmitting coil perpendicular to it. The vertical distance between each near-zero magnetic permeability metamaterial unit cell and the transmitting coil is 2.5 mm, and the horizontal distance is 10 mm; place the designed 1 negative magnetic permeability metamaterial unit cell vertically and horizontally in the middle of the transmitting coil and the receiving coil, just combining with the 4 near-zero magnetic permeability metamaterial unit cells to form a cube three-dimensional hybrid permeability metamaterial.

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